1. Field of the Invention
The present invention relates to an optical communication system, and more particularly to an optical cross-connect system for demultiplexing/switching wavelength-division-multiplexed optical signal channels received via input optical fibers, performing a wavelength division multiplexing on the optical signal channels, and then outputting the resultant signal to output optical fibers.
2. Description of the Related Art
Following the current trend of rapidly growing wavelength division multiplexing techniques using several wavelengths within one optical fiber, it is possible for one optical fiber to transmit a plurality of very high-speed mass storage optical signals. Conventional techniques for fabricating optical components generally use a path setup function, a distribution function (i.e., a switching function) and an add/drop function (i.e., a coupling function) of optical signals that is performed in an optical layer. Given these conventional techniques, an optical communication network on the basis of such wavelength division multiplexing (WDM) techniques can be constructed.
A wavelength division multiplexing (WDM) optical communication network is typically constructed as a mesh-structure network using an optical cross-connect system. The optical cross-connect system that distributes optical signals according to their wavelengths can be adopted for nodes of such optical communication networks. Optical paths for such optical communication networks are determined by a signal distribution state of the optical cross-connect system. In this case, it is necessary to develop simple and economical optical cross-connect systems to manage efficiently and economically the WDM optical communication network. For definitional purposes, the term ‘distribution’ is used as a generic term encompassing both a routing concept and a switching concept.
FIG. 1 is a diagram illustrating a conventional 2×2 optical cross-connect system.
In FIG. 1, a conventional 2×2 optical cross-connect system 100 have two input terminals and two output terminals includes two 1×N wavelength division demultiplexers 110. The demultiplexers 110 demultiplex optical signals, where a plurality of wavelengths λ1, λ2, λ3, . . . , λN, received via the input terminals are wavelength-division-multiplexed. The system 100 also includes N optical switches 120 that receive the same wavelengths of signals from the two wavelength division demultiplexers. The optical switches 120 perform a distribution function for distributing the received signals to a desired output port. The output ports provide the signals to two N×1 wavelength division multiplexers 130 that multiplex signals received from the optical switches 120.
In 2×2 optical cross-connect system 100, the wavelength division demultiplexers 110 classify a plurality of multiplexed optical signals received from input terminals according to their wavelengths, and output the classified signals to an appropriate optical switch 120 corresponding to each wavelength. Each of the optical switches 120 receives optical signals of a specified wavelength related to its own operable range from the wavelength division demultiplexers 110. The optical switches 120 then perform an add/drop operation (i.e., a coupling operation) on the optical signals or passes the optical signals. The resulting signals are distributed to the output ports. Each of the wavelength division multiplexer 130 receives optical signals having different wavelengths from the optical switches 120, wavelength-division-multiplexes the optical signals, and then outputs them via the output terminals.
Arrayed-waveguide gratings (AWGs) are typically used as a multiplexer and a demultiplexer, because they have easily extensible optical signal channels, are simply controlled, and have superior degrees of integration. In case of implementing a conventional 2×2 optical cross-connect system, four 1×N AWGs are needed. As can be seen from FIG. 1, the four 1×N AWGs should be controlled to have the same operational characteristics because 2N wavelengths in total are normally multiplexed and demultiplexed.
Likewise, in the case where N optical signals are transmitted on one fiber, 2M 1×N-AWGs are needed to control an optical cross-connect system having N input optical fibers and N output optical fibers, and N M×M optical switches are also needed. In this case, 2M 1×N-AWGs should be controlled to have the same wavelength transmission characteristics. As will be appreciated, such conventional optical cross-connect systems are complex and incur high production costs due to many requisite components.
Accordingly, there is a need in the art for improved optical cross-connect systems that use fewer AWG and thereby reducing cost and complexity of the systems.